Psychosis is a common behavioral complication of dementia in the elderly, and of Alzheimer's disease (AD) in particular. Although certain limbic structures have been implicated in the cognitive and emotional abnormalities of chronic idiopathic psychosis, little is known about the neuropathological and neuroradiological correlates of psychoses of later onset, including those associated with neurodegenerative disorders. MRI provides the anatomical resolution necessary for in vivo detection of structural abnormalities and has the advantage over neuropathologic data in that results may be correlated with concurrent clinical assessments. The aim of the present study is to use computer-analyzed MR to estimate volumes of specific cerebral structures in AD patients with and without psychosis in an attempt to identify a possible anatomical substrate of late-onset psychosis. Analysis is proposed on four groups of patients (AD with psychosis, AD without psychosis, Lewy body variant, controls). It is our hypothesis that AD subjects with psychosis will demonstrate similar structural abnormalities with regard to their psychosis, especially involving lenticular, frontal and mesial temporal lobe structures. In the Lewy body variant of AD, where extrapyramidal features are characteristic of the clinical presentation, involvement of basal ganglia structures would be expected to be significantly more prominent. If patients die and have autopsies during the time-frame of the study, neuropathological findings will be correlated with quantitative MR analysis.